Shetland Isles SMR

Location and physical characteristics

Shetland Isles SMR



Figure 1: Shetland Isles Scottish Marine Region.The thicker white line delineates the extent of the Shetland Isles SMR. For a map of all SMRs and OMRs, see Figure 5 here

Coastline length (km) 2,382
Sea area (km2 12,309
Deepest point (m) 188
Shallowest point (m) coastline
Average depth (m) 93
Tides (m) 0.0 – 2.0
Salinity 35.20 – 35.30
Sea surface temperature (°C) 7.6 – 13.6

The Shetland Isles SMR includes the northernmost islands in Scottish waters (Figure 1). Throughout the Shetland Isles SMR there is a relatively small spring tidal range (see also Sea level and tides assessment). Intensified tidal currents exist where topography constrains the flow, between the various islands. There is no significant local freshwater input and the occurrence of oceanic waters of Atlantic origin result in generally high salinities in this SMR. The residual circulation close to the islands is clockwise, but the SMR also includes one of the major inflow branches to the North Sea through the Fair Isle Gap. The North Atlantic swell influences the surface wave climate in this SMR, some coasts are extremely exposed but due to the topography some areas, especially the innermost parts of various voes, are extremely sheltered.

Holocene (current geological epoch) sea-bed sediments

Muddy-sands and sandy-muds occur in the more sheltered bays and voes around the islands. The largest deposits occur in St Magnus Bay Basin, Fetlar Basin and Unst Basin. Close to the islands, carbonate or shell-rich gravels and gravelly-sands occur, reflecting the rich nearshore marine fauna. Further offshore sands predominate.

Pleistocene geology

Pleistocene deposits are thin and patchy to the east and west south west of Mainland Shetland, where it is not uncommon for bedrock to outcrop on the sea floor. The more significant Pleistocene deposits tend to occur in distinct basins and locally reach considerable thicknesses of up to 60 m. Deposits in the St Magnus Bay Basin and Fetlar Basin consist predominantly of soft, olive-grey clays rich in hydrogen sulphide, underlain by grey till. The soft clays are probably post-glacial. In the West Fair Isle and Unst Basins compact grey clays with scattered pebbles are the dominant sediment type. Elsewhere in the West Shetland Basin and to the north of the Unst Basin, Pleistocene deposits consist mainly of compact grey clays with scattered pebbles throughout, which are probably tills. These deposits thicken to the north west and north east respectively. Occasionally soft red muds, thought to be slightly older than the soft grey sulphide-rich muds, occur on the East Shetland Platform.

Solid (pre-Quaternary) geology

Offshore much of the solid geology of the sea bed is concealed by sediments, but in areas where these are thin, rocky outcrops do occur. Precambrian metamorphic rocks dominate the sea bed closest to the islands, as they do onshore. However, younger sedimentary rocks such as Devonian and Permo-Triassic sandstones and shales overlie the metamorphic rocks further offshore, especially to the east and south. To the north west of Shetland a northeast trending fault creates a sharp boundary between the ancient basement rocks and young Tertiary sediments.

Productive

Fishing and aquaculture (starting in the latter stages of the 20th Century) have both been, and continue to be, a feature of life in the Shetland Isles SMR. For example, 35,947 tonnes of Atlantic salmon were produced in the Shetland Isles SMR in 2018 with a value of £202 million. This was 23% of all Atlantic salmon produced in Scotland in 2018. Tourism is also important to the Shetland Isles SMR, with many tourists arriving by ferry. As an island-community, the sea is very much a part of Shetland life.

The Productive Assessment was been undertaken, with a focus on 2014 – 2018, on a sectoral basis. For a number of Sectors, including seaweed harvesting and cultivation, oil and gas and aggregates, there was no activity within the Shetland Isles SMR during the period 2014 – 2018. However, for many sectors, there were changes over the period 2014 – 2018 (Figure 2).



Figure 2: Changes that have taken place in the Shetland Isles SMR by Sector. Although the period 2014 – 2018 inclusive has been used where possible, there are some entries when a slightly different time period has been used.Trend data (2014-2018) for the fishing sector for Shetland Isle SMR are not available, therefore data on local authorities which fall within this SMR have been used.

Pressures from human activities

As part of SMA 2020, an assessment of the main pressures from human activities in each of the Scottish Marine Regions and Offshore Marine Regions was undertaken through a MASTS-led workshop. The process and outcomes are presented in detail in the Pressure from Activities section. Five main pressures identified for the Shetland Isles SMR ordered as per the MASTS-led Pressure Assessment Workshop were:

Priority [1] Pressure (FeAST classification) [2] Main healthy and biologically diverse components affected [3] Main contributing FeAST activity /activities to pressure [4] Associated productive assessments [5]
1 Removal of target species (including lethal)
  • Fishing - Bottom otter trawling and pair trawls (OTB, OTT, PTB, TB, TBN)
  • Fishing - Creeling and potting (FPO)
  • Fishing - Line fishing (hand and mechanized line and longlining) (LHP, LHM, LL, LLS)
  • Fishing - Pelagic trawling & purse seining (OTM, PTM, TM, PS, PS1, PS2)
  • Fishing - Scallop dredging (DRB)
2 Sub-surface abrasion/penetration
  • Fishing - Bottom otter trawling and pair trawls (OTB, OTT, PTB, TB, TBN)
  • Fishing - Scallop dredging (DRB)
2 Surface abrasion
  • Fishing - Bottom otter trawling and pair trawls (OTB, OTT, PTB, TB, TBN)
  • Fishing - Creeling and potting (FPO)
  • Fishing - Scallop dredging (DRB)
4 Organic enrichment
  • Aquaculture - Finfish
  • Aquaculture - Shellfish
5 Removal of non-target species (including lethal)
  • Fishing - Bottom otter trawling and pair trawls (OTB, OTT, PTB, TB, TBN)
  • Fishing - Creeling and potting (FPO)
  • Fishing - Line fishing (hand and mechanized line and longlining) (LHP, LHM, LL, LLS)
  • Fishing - Recreational Fishing
  • Fishing - Scallop dredging (DRB)

Clean and safe

The assessments cover eutrophication, hazardous substances, marine litter, noise and microbiology and algal toxins which have the potential to impact on habitats and species as well as being a consequence of human activity. Although sources of litter or contaminants may be local, there are cases when the source is some distance from the impacted area. The main findings for the Shetland Isles SMR are:

Eutrophication

There was no evidence of eutrophication as a consequence of nutrient enrichment. Nutrient inputs showed a decreasing trend as a result of a steady decrease in loads from marine pen fish farms. Winter nutrient concentrations and chlorophyll concentrations were below assessment criteria and relatively stable. In addition, dissolved oxygen concentrations were above levels required to maintain healthy marine ecosystems.

Hazardous substances

Hazardous substances (polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and heavy metals (Hg, Cd and Pb)) assessments in sediment and biota (fish and shellfish) were undertaken at the scale of the five Scottish biogeographic regions: Atlantic North-West Approaches, Irish Sea (Clyde and Solway), Minches and Western Scotland, Scottish Continental Shelf and Northern North Sea.The Shetland Isles SMR is in the Northern North Sea (east Shetland) and Scottish Continental Shelf (west Shetland)  biogeographic regions. There are limited biota and sediment sites in the Scottish Continental Shelf but more sites in the Northern North Sea, with some of these sites being in the Shetland Isles SMR. Contaminant concentrations in the Shetland Isles SMR sites were typical of the Scottish Continental Shelf and Northern North Sea, being generally above background but below concentrations where adverse effects could occur and there were no increasing trends.

A number of biological effects were also measured and assessments undertaken at the scale of the five Scottish biogeographic regions including imposex in dog whelks, an indicator of TBT contamination. There are a number of imposex sites in the Shetland Isles SMR, however, most of them are included in a specific survey covering Sullom Voe and Yell Sound. All the sites in the Shetland Isles SMR indicate that concentrations of TBT in the marine environment are at background or not causing significant harm. The other contaminant-specific biological effects (PAH bile metabolites and 7- ethoxyresorufin O-deethylase (EROD) activity) in the Northern North Sea biogeographic region were consistent with the hazardous substances and showed a limited exposure to contaminants. One site in Shetland (west) was assessed for EROD and was at background levels.

External fish disease, a general measure of fish health, was assessed at two sites in the Shetland Isles SMR, and showed that the fish health status was satisfactory.

Marine litter

Due to the lack of assessment criteria for marine litter, beach litter and microplastic, status assessments were not possible. However, litter and microplastics are present in all SMRs, including the Shetlands Isles SMR. The Shetland Isles SMR has a relatively low concentration of microplastics in surface water (< 5,000 microplastics per km2 of sea surface).

Seafloor litter was assessed at the scale of the biogeographic regions; The Shetland Isles SMR is in the Northern North Sea (east Shetland) and Scottish Continental Shelf (west Shetland) biogeographic regions. There have been apparent decreases in seafloor litter density over time between 2012 to 2018 in the Scottish Continental Shelf biogeographic region, but no trend in the Northern North Sea biogeographic region.

The Da Voar Redd Up is Shetland’s annual beach clean but the data are recorded in a different way to that of the Marine Conservation Society therefore was not included in the beach litter assessment.The Da Voar Redd Up is Shetland’s annual beach clean but the data are recorded in a different way to that of the Marine Conservation Society therefore could not be used here.The Da Voar Redd Up is Shetland’s annual beach clean but the data are recorded in a different way to that of the Marine Conservation Society therefore could not be used here.

Noise

There are limited noise data for the Shetland Isles SMR; no continuous noise data were collected and there were very few impulsive noise data for this region. It is not possible to do a status assessment as there are no assessment criteria to say what levels of noise are harmful, and not enough years of data to carry out a trend assessment.

Microbiology and algal toxins

Escherichia coli is monitored in shellfish as a proxy of the microbiological quality of the water from shellfish production areas. Classifications are awarded according to the Food Standards Scotland (FSS) Protocol for Classification and Management of Escherichia coli. A site can be designated A, B, C, A/B or B/C, with Class A products able to go direct for human consumption. The majority of production areas in the Shetland Isles SMR were in the highest class (A, 89%), and no areas had prohibited levels of Escherichia coli.

A number of marine algal species produce biotoxins which, by accumulation in bivalve molluscs such as mussels and oysters, can cause human illness when these shellfish are eaten. Both biotoxins and phytoplankton are routinely monitored in classified shellfish production areas under Regulation (EU) 2017/625. Such monitoring takes place at several sites within the Shetland Isles SMR. Concentrations of diarrhetic shellfish toxins (DSTs) exceeded regulatory limits (RL) in every year between 2010 and 2018. An exceptionally high concentration of DSTs was recorded in mussels in July 2013. This was linked to 70 reported cases of diarrhetic shellfish poisoning. Dense blooms of Dinophysis sp. (a phytoplankton species associated with DST production) were observed in the Shetland Isles SMR in 2013, 2016 and 2018. Paralytic shellfish toxins above RL were reported in 2013, 2014 and 2018, and no samples exceeded RL for amnesic shellfish toxins.

Healthy and biologically diverse

This section summarises the information from the Marine Protected Areas (MPAs) and intertidal and continental shelf habitats assessments from SMA2020. It also provides information from the relevant case studies relating to Priority Marine Features (PMFs), with a focus on habitats.  Further work is required to enable assessment at a regional scale for most species; this will be included in Scotland’s next marine assessment.

At a regional scale for MPAs the focus is on the number of new MPAs, MPAs with new spatial management measures, and MPAs in which spatial management measures are in discussion, as well as recognising monitoring that has been undertaken between 2012-2018.  For the marine habitats, the focus is on interpreting the relevant intertidal and continental shelf habitat assessments – biogenic habitats, predicted extent of physical disturbance to the seafloor  (BH3) and intertidal seagrass beds.  For PMFs, a summary is provided of the changes in our understanding of the habitats of most relevance to the Sheltand Isles SMR, including changes in distribution and extent.

Marine Protected Areas

Progress in developing the Scottish MPA network

There are 25 MPAs in the Shetland Isles SMR that contribute to the Scottish MPA network (see Table 1).  Some of these MPAs overlap completely or partially in terms of their spatial coverage and/or the features (habitats, species, etc.) they were set up to help conserve.  They are counted as separate MPAs because they have been established under different legislation which influences the way in which they are managed.  Also note that there are MPAs that straddle the boundaries between different SMRs/OMRs.  Where this is the case, these MPAs have been counted as contributing to the MPA network in all of the SMRs/OMRs in which they are present.  This means that the total number of MPAs in Scotland cannot be calculated through combining the SMRs/OMRs totals.  Please see the Marine Protected Area assessment which contains statistics for the Scottish MPA network as a whole.  

Table 1. Numbers of types of MPAs in the Shetland Isles SMR that contribute to the Scottish MPA network, including number of new MPAs introduced since 2012.

Type of MPA

Abbr.

Total no. of MPAs

No. of new MPAs 2012-2018

Demonstration & Research MPA

D&R MPA

1

1

Historic MPA

HMPA

1

1

Nature Conservation MPA

MPA

2

2

Ramsar

-

0

0

Site of Special Scientific Interest

SSSI

7

0

Special Area of Conservation

SAC

7

1*

Special Protection Area

SPA

7

0

Note that in December 2020 there were another three SPAs designated in this SMR in addition to those in the table above (i.e. Bluemull and Colgrave Sounds, East Mainland Coast, Shetland and Seas off Foula).

Highlights from the various MPAs include:

The MPAs in Shetland Isles SMR cover a wide range of natural heritage features including birds, marine mammals, fish, benthic and intertidal habitats, and geomorphological features, as well as the only Demonstration and Research MPA in Scotland – Fair Isle.  The high energy environment and spectacularly clear waters of Fetlar to Haroldswick MPA are the perfect combination for maerl beds, kelp and seaweed communities, shallow tide-swept sands with burrowing bivalves, and horse mussel beds to thrive. Birds from one of Scotland’s largest colonies of breeding black guillemots (> 2000 individuals) forage over these rich seabed habitats.  The Mousa to Boddam MPA contains the most consistent and reliable sandeel recruitment areas in the SMR.  The sandeel populations (and fishery) here are dependent upon an influx of young fish (less than one year old) from a large spawning area situated to the west and north of Orkney.  Mousa SAC, off the east coast of Shetland Mainland, supports one of the largest groups of harbour seal in the SMR; the large rocky tidal pools on the island are of particular importance, as they are frequently used by the seals for pupping, breeding and moulting.  The SAC is also designated for its reefs and submerged or partially submerged sea caves.  The Vadills SAC, at the head of Brindister Voe is an outstanding example of a complex lagoon system supporting a wide range of communities with a high diversity of species. It comprises a number of shallow basins and has examples of both lagoonal inlets and silled lagoons. This extremely sheltered, undisturbed and natural environment has a gradation of habitats from brackish to fully marine conditions, with still too fast-flowing water, and soft, flocculent, peaty-mud through coarse sediments including maerl to bedrock and boulders.  The Shetland Isles SMR is important for its populations of breeding seabirds and wintering waterbirds, and has a large number of SPAs, including Foula SPA which is important for a wide range of breeding seabirds and is one of only seven known nesting localities in the EU for Leach’s petrel. Both the Mousa to Boddam MPA and the Fetlar to Haroldswick MPA sit within the Shetland carbonate production area, a key geodiversity area in Scottish waters. The Shetland carbonate production area is an internationally important example of a non-tropical shelf carbonate system. These sediments supply the carbonate sands to the coastal machair around Shetland which supports specific and diverse grassland vegetation and is one of the rarest habitats in Europe.



Progress in managing MPAs

The progress in implementing management for MPAs in the Shetland Isles SMR is summarised in Table 2.  This includes information on where spatial management measures are in place and where they are under discussion.  It also includes information on the number of MPAs that have been monitored, whether by statutory bodies or through citizen science.

Table 2. Summary of progress in managing Marine Protected Areas in the Shetland Isles SMR. Note that the spatial measures listed in the table are in addition to the protection provided as a result of consideration of activities/developments through licensing and consenting processes. Also, the monitoring of mammals and habitats within SSSIs and SACs has been split out to reflect the different programmes of work.  These figures cannot be added together to provide a total number of SSSIs and SACs in which monitoring took place because of overlaps in coverage.  

Type of MPA

Spatial measures in place pre-2012

New spatial measures in place 2012-2018

Spatial  measures in discussion 2012-2018

No. of MPAs monitored by statutory bodies 2012-2018

No. of MPAs monitored via citizen science 2012-2018

Historic MPA

N/A

0

0

1

0

Nature Conservation MPA

N/A

1

2

1

0

Site of Special Scientific Interest

0

0

0

Mammals

3

Mammals

0

Special Area of Conservation

0

2

4

Mammals

3

Mammals

0

Habitats

2

Habitats

0

Special Protection Area

0

0

0

6

0

Within the Shetland Isles SMR there are currently no specific fishing orders or Marine Conservation Orders in place for MPAs. However, the Shetland Shellfish Management Organisation has put restrictions on scallop dredging in certain parts of Fetlar to Haroldswick MPA, Sullom Voe SAC and The Vadills SAC to protect sensitive habitats including  maerl beds and horse mussels.  Further management measures  of various fishing activities are under discussion for Fetlar to Haroldswick MPA, Mousa to Boddam MPA, Mousa SAC, Papa Stour SAC and Sullom Voe SAC.

During this assessment period the majority of the MPAs have been monitored at least once by the statutory bodies, and some have had multiple visits.  Monitoring has covered seabirds, subtidal habitats, otters and seals.  Seal monitoring continues to be undertaken via a collaboration between the Sea Mammal Research Unit, NatureScot and other partners.

Information on MPA boundaries can be viewed in Marine Scotland’s NMPi. To find out more about specific MPAs, please visit NatureScot’s SiteLINK.  Detailed reports on habitat monitoring are referenced in Further reading – seabed habitat monitoring reports.

Intertidal and continental shelf habitats

SMA2020 contains three relevant habitat assessments: intertidal seagrass beds, subtidal biogenic habitats, and predicted extent of physical disturbance to seafloor.  Assessment of the status of subtidal biogenic habitats is based on temporal reductions in extent of six habitat types: seagrass beds, serpulid aggregations, flame shell beds, maerl beds and horse and blue mussel beds.  Although beds of subtidal seagrass, maerl, blue mussels and horse mussels have been recorded within the region, no data are available on temporal changes in extent of these habitats and hence no status assessments could be made.  There are no records of flame shell beds or serpulid reefs.  There is only a single record of an intertidal seagrass bed in the region, so no status assessment of the habitat could be completed for SMA2020, as this is dependent upon the availability of time series data.  Modelling work was carried out as part of the assessment to predict the extent of physical disturbance to the seafloor more generally.

Predicted physical disturbance to the seafloor

To assess physical disturbance to seafloor habitats SMA2020 employed a modelling approach which generates a map of predicted relative disturbance levels from demersal fishing activity on a scale of 0 (zero) to 9 (severe).  The map was produced by the combination of information on the distribution of habitats, the sensitivity of the habitats (and species present to varying degrees) and the fishing pressure from demersal trawling, dredging and seine netting.  Fishing pressure information was derived from Vessel Monitoring System (VMS) data from 2012 - 2016 and was categorised as either surface abrasion (disturbance of surface and upper layers of sediment) or sub-surface abrasion (disturbance to a depth of >3 cm).  The final predicted disturbance index utilises the greater of these two pressure values and for descriptive purposes has been categorised as no disturbance (0), low disturbance (1-4) and high disturbance (5-9).

It should be emphasised that this method does not measure disturbance to seabed habitats, but predicts relative levels of disturbance. These relative levels are dependent upon the accuracy of habitat data and sensitivity assessments.  Many of the habitat data are derived from modelling and there is a low level of confidence in its accuracy.  Geographical variation in the accuracy of the sensitivity information employed is likely to be great, being dependent upon the level and quality of information used locally.  A significant limitation of the method is that during the assessment period pressure data were only available for vessels >12 m, which has probably resulted in an underestimation of disturbance.

Predicted habitat disturbance by mobile demersal fishing for the Shetland Isles SMR is the highest for all SMRs in terms of the proportion of the seabed with 80% high disturbance compared to an average of 50% and at 4% has the smallest proportion of the seabed predicted to experience no disturbance (average of 12% for all SMRs) (Figure 3).  High disturbance levels occur particularly around the north of the archipelago and to the south west and south, where the sea bed is dominated by coarse sediments.  These predicted levels closely correspond to the sensitivity of the habitat to surface abrasion, as well as the surface fishing pressure.